Supporting structure of optical element, exposure apparatus having the same, and manufacturing method of semiconductor device

ABSTRACT

A supporting structure for supporting an optical element includes a first supporting member for supporting the optical element, and a second supporting member for supporting the first supporting member. The value of a thermal expansion coefficient of the first supporting member is between those of the optical element and the second supporting member.

This is a divisional application of U.S. patent application Ser. No.09/817,018, filed Mar. 27, 2001, now U.S. Pat. No. 6,867,848.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a supporting structure of opticalelements, an optical apparatus such as an exposure apparatus constructedby using the supporting structure, and a method for manufacturing asemiconductor device by using the optical apparatus, etc., and inparticular relates to a supporting member for supporting an opticalelement such as a lens and a mirror, and an optical apparatus with ahigh degree of accuracy which comprises the supporting member forsupporting the optical element, the optical apparatus being an exposureapparatus for use in manufacturing semiconductor integrated circuits,for example.

2. Description of the Related Art

A semiconductor exposure apparatus is an apparatus for transferring anegative plate (reticle) having a circuit pattern onto a substrate(silicon wafer). During the transferring, a projection lens is used forforming an image of the reticle pattern on the wafer, and highresolution of the projection lens is required for forming a highlyintegrated circuit. Accordingly, the lens for the semiconductor exposureapparatus is supported to have small aberration.

In view of such conditions, lenses for the semiconductor exposureapparatus demand uniformity in various characteristics of glass andfilms and high processing accuracy of a glass figure and assemblingaccuracy.

A lens barrel for holding glass used for lenses is generally made from ametal and materials different from glass are used therefor.

FIG. 11 illustrates part of an optical system of a conventionalsemiconductor exposure apparatus and shows a structural concept of thelens barrel. In the drawing, plural lenses 101 and 102 are fixed tometallic frames 103 and 104 for holding the lenses, which are furtherplaced within a supporting member 105 and are urged and fixed theretofrom upward movement by retaining screw-rings 107 and 108, respectively.

However, in the structure of the conventional lens barrel mentionedabove, upon changing of ambient temperature, since the lenses and lensbarrel elements respectively change in shape, the aberration thereof maychange. In an exposure apparatus especially using a light source with ashort wavelength, lenses are made from quartz or fluorite; sincematerials of the lenses and the lens barrel elements differ in thethermal expansion coefficient from each other, they cannot expand orshrink simply and freely without restriction from outside, respectively;consequently, the lens figure largely changes, thereby such deformationdue to temperature changes largely affects the aberration of the lenses.Plural supporting members 105 are generally overlaid one on another tobe arranged in the axial direction; when an external force is appliedthereto during the connection thereof by overlaying or due to otherreasons, the metallic frame for holding the lens is pressurized so thatthe lens is subjected to an external force from the screw-rings, etc.,thereby deforming the lens figure, resulting in degraded performance ofthe optical system.

Also, in the conventional example mentioned above, the lens placedwithin the inner radius of the metallic frame becomes deformed due togravity; by reasons that the direction and amount of such deformationdepend on the figure of a lens placing portion and it is difficult toprocess the planar figure of the lens placing portion with a higheraccuracy than that of the lens, and it cannot be assumed in advance thathow the lens abutting the lens placing portion becomes deformed becauseeach workpiece of the portion differs from one another, it is necessarythat various kinds of aberration be corrected by predeterminedadjustment of the lens posture or positions after checking the opticalperformance in the assembled optical system, which requires highaccuracy in the deformation, resulting in an increased number of stepsfor assembly and adjustment.

In order to solve such problems, Japanese Patent Laid-Open No.2000-66075 discloses that a lens is supported at plural points and therotational angle of an optical element is adjusted so as to reduce theaberration of the entire optical system, which results from each opticalelement deformation produced by the lens support. However, in thisstructure, it is known that upon changes in ambient temperature, thelens surface is deformed due to the thermal expansion coefficientdifference between the lens and the metallic frame (when the lens issupported with three-point supporting, the 3θ deformation sensitivelychanges relative to the temperature), so that the desired opticalperformance cannot be obtained.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide, bysolving the conventional problems described above, a supportingstructure of optical elements, which can reduce the lens surfacedeformation due to the strain produced by changes in ambient temperatureand during the assembling so as to obtain a stable high resolution withsmall aberration, an optical apparatus such as an exposure apparatusconstructed by using the supporting structure, and a manufacturingmethod of a semiconductor device, etc., using the apparatus.

In accordance with a first aspect of the present invention, there isprovided a supporting structure for supporting an optical elementcomprising: a first supporting member for supporting the opticalelement; a second supporting member arranged in the outer diameter sideof the first supporting member for supporting the first supportingmember; and an elastic member placed between the first supporting memberand the second supporting member in the radial direction, the innerdiameter side of the elastic member being connected to the firstsupporting member while the outer diameter side of the elastic memberbeing connected to the second supporting member, the elastic memberbeing elastically deformable in the radial direction, wherein the firstsupporting member does not contact the second supporting member in theaxial direction.

In accordance with a second aspect of the present invention, there isprovided an exposure apparatus comprising: an illuminating opticalsystem for illuminating a reticle with a light beam from a light source;and a projection optical system for projecting a light beam from thereticle on a wafer, wherein the illuminating optical system and/or theprojection optical system have a supporting structure for supporting anoptical element according to the first aspect of the present invention.

In accordance with a third aspect of the present invention, there isprovided a method for manufacturing semiconductor devices comprising anexposing step performed by an exposure apparatus according to the secondaspect of the present invention.

In accordance with a fourth aspect of the present invention, there isprovided a supporting structure for supporting an optical elementcomprising: an optical element; a first supporting member for supportingthe optical element; and a second supporting member for supporting thefirst supporting member, the second supporting member being made from amaterial different from that of the first supporting member, wherein thethermal expansion difference between the optical element and the firstsupporting member is smaller than the thermal expansion differencebetween the optical element and the second supporting member.

In accordance with a fifth aspect of the present invention, there isprovided a supporting structure for supporting an optical elementcomprising: an optical element made from fluorite; a first supportingmember for supporting the optical element; and a second supportingmember made from a material different from that of the first supportingmember, wherein the thermal expansion difference between the opticalelement and the first supporting member is within ±10%.

In accordance with a sixth aspect of the present invention, there isprovided a supporting structure for supporting an optical elementcomprising: a plurality of optical elements; a plurality of firstsupporting members for respectively supporting the plurality of opticalelements; and a plurality of second supporting members for respectivelysupporting the plurality of first supporting members via structureshaving elasticity in the radial direction of the optical element.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of a structure of a lens supporting member accordingto a first embodiment of the present invention;

FIG. 2 is a drawing of part of the structure of the lens supportingmember according to the first embodiment of the present invention;

FIG. 3 is a drawing of a structure of a lens supporting member accordingto a second embodiment of the present invention;

FIG. 4 is a drawing of a structure of an exposure apparatus forsemiconductors according to a third embodiment of the present invention;

FIG. 5 is a drawing of a structure of a lens supporting member accordingto a fourth embodiment of the present invention;

FIG. 6 is a drawing of part of the structure of the lens supportingmember according to the fourth embodiment of the present invention;

FIG. 7 is a detail view showing part of the connection portion of asecond supporting member according to the fourth embodiment of thepresent invention;

FIG. 8 is a drawing of a structure of a lens supporting member accordingto a fifth embodiment of the present invention;

FIG. 9 is a drawing of a structure of a lens supporting member accordingto a sixth embodiment of the present invention;

FIG. 10 is a schematic illustration of an exposure apparatus forsemiconductors according to a seventh embodiment of the presentinvention; and

FIG. 11 is a drawing of a conventional lens holding member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention, which discloses a supportingstructure of optical elements, an optical apparatus such as an exposureapparatus constructed by using the supporting structure, and amanufacturing method of manufacturing a semiconductor device, etc.,using the apparatus, can reduce the unnecessary lens surface deformationdue to the strain produced by changes in ambient temperature and duringthe assembling so as to obtain stable, high resolution with smallaberration by virtue of the above-mentioned structure. For example, useof the above-mentioned structure reduces the deformation produced in anoptical element by the thermal strain due to ambient temperature changesin the optical apparatus and a temperature increase in the opticalelement by light energy absorption. Using the structure also reduces thedifference in the thermal expansion coefficient so as to decrease thethermal deformation of the optical element. Furthermore, using thestructure reduces the stress produced when an elastic portion absorbsthe thermal deformation difference between a first supporting member anda second supporting member, thereby improving the efficiency inabsorbing the deformation. Since, by using the structure, aneccentricity of the optical element is prevented or the unnecessarythermal deformation affecting the optical element can be symmetrizedabout the axis even though it is very small, the inverse effectaffecting the optical performance can be effectively reduced. Also, byusing the structure, an optical apparatus or manufacturing apparatus formanufacturing semiconductors, etc., can be achieved so as to havestable, high resolution with small aberration.

EMBODIMENT

Embodiments according to the present invention will be described below.

(First Embodiment)

In a first embodiment, a supporting member of a lens is formed by usingthe above-mentioned structure, and FIG. 1 shows a half of opticalelements according to the embodiment.

The drawing shows a quartz lens 1 and the lens supporting member 11 madefrom invar, which is a nickel alloy having a thermal expansioncoefficient substantially identical to that of quartz. In addition, thelens 1 is fixed to the supporting member 11 by adhesion.

A supporting member 3 coaxially supports lenses and is made from iron.

In the peripheral portions of the supporting member 11, plural cut-outsare formed so as to arrange elastic member 12 therein, which are leafsprings. In the elastic member 1, both plate ends are connected to thesupporting member 11 while the center thereof is connected to thesupporting member 3. By this supporting structure, the elastic member 12has small elasticity relative to the optical elements in the radialdirection.

The drawing also shows a fluorite lens 2 and a supporting member 21 forsupporting the lens 2, which is brass, a copper-zinc alloy havingsubstantially the same thermal expansion coefficient as that offluorite.

The lens 2 is also bonded to the supporting member 21. An elastic member22 is identical with the elastic member 12.

FIG. 2 shows part of the lens supporting members shown in FIG. 1 andpositions in one lens unit, in which the elastic members are attached.As shown in the drawing, plural elastic members 12 are arranged atsubstantially the same angular pitches in the periphery of thesupporting member 11 and both ends 12 a thereof in the inner diameterside of the supporting member 11 are connected to the supporting member11 with screws. The elastic member 12 is connected to the supportingmember 3 with screws at the central position 12 b in the outer diameterside of the supporting member 11. The supporting member 11 does notcontact the supporting member 3 in the axial direction, so that theweight of the supporting member 11 is supported by the elastic members12.

The material of the elastic member 12 is preferably identical to that ofthe supporting member 11; however, it may be another material such as ametallic material for springs such as stainless steel and a non-metallicmaterial such as zirconium. This is because when the rigidity of thesupporting member 11 is much higher than that of the elastic member 12,the thermal strain due to the thermal expansion coefficient differencebetween both the materials does not have a serious influence on theentire system. Similarly, the material of the elastic member 22 ispreferably identical to that of the supporting member 21; however, itmay be another material. FIG. 2 illustrates the case that three elasticmembers are arranged; the number of elastic members is preferably three;however, it is not limited to this; it may be two or more. In any case,in circumferences of the supporting members 11 and 21, the elasticmembers 12 and 22 are respectively arranged at equal intervals so thatthe eccentricity of the supporting members 11 and 21 due to the thermalstrain can be prevented.

In a lens barrel of such a structure, upon changes in ambienttemperature, the supporting members 3 and 11 expand or shrinkdifferently from each other due to the thermal expansion coefficientdifference between both the materials; however, the bending deformationof the plate-shaped spring portion of the elastic member 12 absorbs thethermal expansion difference, so that the supporting member 11 cansimply expand or shrink substantially freely.

The thermal expansion coefficients of the quartz lens 1 and the fluoritelens 2 are substantially the same as those of the surrounding supportingmembers 11 and 21, respectively, so that the lenses can substantiallysimply expand or shrink, thereby suppressing the surface figure strainwhich is destructive to the optical performance.

The tolerance of the difference between the thermal expansioncoefficient of the lens and that of the surrounding supporting memberdepends on accuracies in ambient temperature of the optical system andthe optical performance required for the optical system.

The optimum materials of the supporting member may be selected inconsideration of these conditions. For example, if these conditionspermit, alumina, ceramic iron may be selected as the material of thesupporting member 11 for the quartz lens, even though these materialshave a thermal expansion coefficient being slightly different fromquartz. In any case, a material having a thermal expansion coefficientbeing closer to that of the lens than that of the supporting member 3may be used for the supporting members 11 and 21, and thereby reducingharmful deformation of the lens surface figure due to temperaturechanges of the lens and increasing the temperature stability of theoptical system. The supporting members 11 and 21 also do not directlycontact the supporting member 3 in axial and radial directions and boththe supporting members 11 and 21 are supported via the elastic members12 and 22, respectively. This means that an external force to thesupporting member 3 or the deformation thereof due to the weight is notdirectly transmitted to the supporting members 11 and 21 so as tosuppress the surface figure strains of the lenses 1 and 2 due to thedeformation of the supporting members 11 and 21.

(Second Embodiment)

FIG. 3 illustrates the structure of a lens supporting member accordingto a second embodiment of the present invention.

The drawing shows a quartz lens 31, a lens supporting member 32 madefrom invar, a rubber adhesive member 33 having elasticity, and a member34 for supporting the lens supporting member 32, which is made fromiron. In the embodiment, just like the first embodiment, the thermalexpansion coefficient of the supporting member 32 is also to be close tothat of the lens 31 and the unnecessary thermal deformation due to thethermal expansion coefficient difference between the supporting members34 and 32 can be relieved by the elasticity of the adhesive 33, enablingthe harmful deformation of the lens surface figure to be reduced.

(Third Embodiment)

FIG. 4 is a schematic diagram of an exposure apparatus, in which thelens supporting member shown in FIG. 1 or 3 is applied to asemiconductor exposure apparatus.

In the exposure apparatus, part of a reticle 40 placed on a reticlestage 41 is irradiated with an illuminating light beam for exposure froman illuminating optical system 44. The illuminating light beam is anexcimer laser beam having a wavelength of 193 nm.

The irradiated region is slit-like and covering part of a pattern regionof the reticle. The pattern corresponding to the slit-like portion isreduced in scale to be a quarter by a projection optical system 42 so asto be projected on a wafer 45 placed on a wafer stage 43. The projectionoptical system 42 is arranged on a frame 46 of the exposure apparatus.

By scanning the reticle and the wafer relative to the projection opticalsystem, the pattern region of the reticle is transferred on sensitivematerials on the wafer. This scanning exposure is repeatedly performedon plural transfer regions (shots).

The projection optical system 42 is required to have high resolution andthe supporting member for the lens thereof is demanded to have astructure with high accuracies. Quartz and fluorite are used for thematerial of the lens.

These lenses are supported as shown in FIG. 1, and in FIG. 1, whennumerals 1 and 2 respectively denote the quartz lens and the fluoritelens, it is preferable that an alloy member 11 is made from invar whichis an alloy of iron and nickel as principal ingredients, and an alloymember 21 is made from an alloy of copper and zinc as principalingredients such as brass.

Both the members preferably have thermal expansion coefficients beingsubstantially identical to those of the lenses to be supported.

A material of the supporting member 11 for supporting the quartz lens 1may be preferably selected from a cordierite material includingmagnesium oxide and silicon oxide, a ceramic material including aluminaand silicon nitride, and a glass material having low thermal expansionwhich is called Zerojule as the trade name.

A material of the member 21 for supporting the fluorite lens 2 may bepreferably selected from an alloy of iron-chromium-nickel such asso-called 18-8 stainless steel, an alloy of copper-tin-phosphorus, whichis called copper or phosphor bronze, an alloy ofnickel-iron-manganese-copper, which is called copper or white copper, analloy of nickel-chromium, and an alloy including aluminum as a principalingredient such as an aluminum die-casting alloy ofaluminum-silicon-copper. When being applied especially to the exposureapparatus, since the energy of a light beam for exposure is absorbed bythe lens so as to generate heat, a copper alloy having a high thermalconductivity is more preferable. The thermal expansion coefficient offluorite is approximately 19 ppm; by simulation, the inventor confirmedthat by using materials having the same coefficient as this value witherrors within ±10%, harmful effects due to temperature on the lens canbe substantially suppressed.

As a material of the supporting member 3, a material having any thermalexpansion coefficient from iron down may be used. By the elastic members12 and 22, the unnecessary deformation of the lens due to the thermalexpansion coefficient difference between materials being different fromeach other can be reduced. When the entire lens system is fixed to theframe 46 of the exposure apparatus body, the strain due to the fixingmay be produced in the lens supporting member 3; however, the elasticmembers 12 and 22 have a function of reducing the strain from affectingthe lens. Therefore, the lens supporting structure with high accuraciescan be obtained, so that a lens system for obtaining resolution requiredfor manufacturing semiconductors can be achieved.

An important thing in the lens supporting structure for use in theexposure apparatus is that the lens itself produces heat in it due to alaser beam for exposure. During the expansion of the lens due to theheat, when the thermal expansion coefficients of the supporting members11 and 21 are substantially the same as those of the lenses, theexpansions of the supporting members 11 and 21 by the thermal conductionto the supporting members are substantially the same as those of thelenses, thereby largely suppressing the harmful strain of the lens.

(Fourth Embodiment)

A fourth embodiment of the present invention will be described withreference to FIGS. 5 to 7. FIG. 5 shows a half of an optical apparatusaccording to the embodiment. The direction of gravity agrees with theoptical axis and is indicated by −Z in the drawing.

FIG. 5 shows a quartz lens 5 and a supporting member 51 for supportingthe lens 5 and having three projections at 120° pitches for supportingperipheral portions of the lens in the gravity direction. The materialof the supporting member 51 is brass in the embodiment. The radialclearance between the periphery of the lens 5 and the supporting member51 is filled with adhesive along the whole circumference, so that thelens 5 is fixed to the supporting member 51. The supporting member 53coaxially supports these lenses and is made from iron. Plural cut-outsare formed in the periphery of the supporting member 51 so as to arrangeelastic members 52 formed by plate springs therein. In the elasticmember 52, both ends of the plate are connected to the supporting member51 and the central portion thereof is connected to the supporting member53. By this supporting structure, the elastic member 52 has smallelasticity relative to the optical elements in the radial direction.

A spacer 54 is a member for adjusting the spacing between lens barrelunits at predetermined intervals in the optical axial direction, eachunit comprising one lens 5, one supporting member 51, one supportingmember 53, and one elastic member 52. As shown in FIG. 7, on the outerperipheries of the supporting member 53 and the spacer 54, holes andtapped holes for fixing with bolts are respectively formed at 60°pitches, so that each lens barrel unit can be arbitrarily rotated at 60°pitches so as to be relatively combined and fixed while each lens barrelunit can be moved and fixed in the direction orthogonal to the opticalaxis by the clearance between the hole for fixing with a bolt and thebolt so as to adjust the unit to desired optical characteristics. Theholes for fixing with bolts are not limited to be at 60° pitches ofcourse; they may be at 30° pitches, 45° pitches, or other degreepitches. Also, by using a structure different from that in theembodiment, which is movable by the clearance between the hole forfixing with a bolt and the bolt, the lens barrel unit may be moved inthe direction orthogonal to the optical axis.

Since each lens 5 is supported by the supporting member 51 at threepoints, gravity deformation of 3θis produced therein in the gravitydirection; the lens barrel unit is rotated about the optical axis at apredetermined angle so as to be fixed so that the aberration produced ineach lens by the gravity deformation is cancelled from the entireoptical system so as to have desired optical performance. In thisembodiment, each lens barrel unit is fixed by relatively shifting it by60°.

FIG. 6 illustrates the arrangement of three elastic members; the numberof the elastic members is preferably three; it is not limited to thisand it may be two or more. In any case, by arranging the elastic members52 in the periphery of the supporting member 51 at equal intervals, theeccentricity of the supporting member 51 due to the thermal strain canbe prevented.

In a lens barrel of such a structure, upon changes in ambienttemperature, the supporting members 53 and 51 expand or shrinkdifferently from each other due to the thermal expansion coefficientdifference between both the materials; however, the bending deformationof the plate-shaped spring portion of the elastic member 52 absorbs thethermal expansion difference, so that the supporting member 51 cansimply expand or shrink substantially freely.

Between the quartz lens 5 and the supporting member 51, there is not aninterposed elastic member for absorbing the thermal expansiondifference, so that upon changes in ambient temperature, expansion orshrinkage is produced therein differently from each other so as todeform the lens figure; however, since the clearance between them isuniformly filled with adhesive along the whole circumference of thelens, it was confirmed by computation and experiments that thedeformation is limited to being very small and being symmetrical aboutthe axis, and the 3θ figure is not changed.

Using such a structure can reduce harmful deformation of the lenssurface figure due to temperature changes of the lens and can improvethe stability of the optical system against temperature changes.

Each lens can be independently rotated and combined about the opticalaxis at a desired angle corresponding to the lens surface figureproduced by the lens gravity deformation and the lens polishing process,and further the eccentricity can be adjusted in a direction orthogonalto the optical axis, enabling the aberration of the optical system tohave a desired degree.

(Fifth Embodiment)

Another embodiment of the present invention will be described below withreference to FIG. 8.

FIG. 8 is a schematic diagram of a structure of a projection opticalsystem according to the embodiment of the present invention.

In FIG. 8, like reference characters designate like functional portionscommon to the embodiments described above.

The direction of gravity agrees with the optical axis and is indicatedby −Z in the drawing.

In FIG. 8, a supporting member 61 for supporting the lens 5 has threeprojections formed at 120° pitches for supporting the lens periphery inthe gravity direction and is made from invar which is a nickel alloyhaving a thermal expansion coefficient being substantially identicalwith that of quartz. The radial clearance between the lens periphery andthe supporting member 61 is filled with adhesive in the vicinities ofthe three projections, so that the lens is fixed to the supportingmember. The coated area of the adhesive is determined by the mass of thelens so as not to move the lens 5 in position when a predeterminedacceleration is applied to the optical system.

Since each lens 5 is supported by the supporting member 51 at threepoints, gravity deformation of the 3 θ is produced therein in thegravity direction, then, the lens barrel unit is rotated about theoptical axis at a predetermined angle so as to be fixed so that theaberration produced in each lens by the gravity deformation is cancelledfrom the entire optical system so as to have a desired opticalperformance. In this embodiment, each lens barrel unit is fixed byrelatively shifting it by 60°.

In a lens barrel of such a structure, just like in the first embodiment,upon changes in ambient temperature, the bending deformation of theplate-shaped spring portion of the elastic member 52 absorbs the thermalexpansion difference between the supporting members 61 and 53, so thatthe supporting member 61 can simply expand or shrink substantiallyfreely.

In the embodiment, the quartz lens 5 is substantially the same in thethermal expansion coefficient as the surrounding supporting member 61,so that the lens can substantially simply expand or shrink, therebysuppressing the production of the surface figure strain which isdestructive to the optical performance.

Also, the adhesive is used for joining the lens 5 to the supportingmember 61 in the embodiment; however, by mechanically pressing the lensperiphery, similar benefits may also be obtained when using thestructure.

According to the embodiment, since the amount of the adhesive to be usedis reduced to the utmost as described above, harmful gas produced fromthe adhesive which will cause the degradation in the optical performancecan be suppressed to the minimum, thereby improving not only thestability of the optical system against the temperature changes but alsothe long term stability thereof.

(Sixth Embodiment)

Another embodiment of the present invention will be described below withreference to FIG. 9.

FIG. 9 is a schematic diagram of a structure of a projection opticalsystem according to the embodiment of the present invention.

In FIG. 9, like reference characters designate like functional portionscommon to the embodiments described above. The direction of gravityagrees with the optical axis and is indicated by −Z in the drawing.

FIG. 9 shows a supporting member 62 for coaxially supporting lens barrelunits which are fixed with bolts to desired positions in the supportingmember 62 by interposing the spacers 54 for adjusting the lens positionin the optical axial direction therebetween.

In the first and second embodiments, the lens barrel units are fixedtogether via the spacers with bolts; in the embodiment, since each lensbarrel unit is fixed to the supporting member 62 having high rigidity,the optical system can be assembled without the interaction between thelens barrel units to apply assembling strain to each other.

In the embodiment, just like in the first embodiment, the supportingmember 51 is made from brass and the entire outer periphery of the lens5 is filled with adhesive; however, of course, just like in the secondembodiment, it may be possible that the thermal expansion coefficient ofthe supporting member is substantially equalized to that of the lens soas to reduce the amount of the adhesive.

(Seventh Embodiment)

FIG. 10 is a schematic diagram of an exposure apparatus, in which thelens supporting structure shown in FIG. 5 is applied to a semiconductorexposure apparatus. In the exposure apparatus, part of a reticle 70placed on a reticle stage 71 is irradiated with an illuminating lightbeam for exposure from an illuminating optical system 74. Theilluminating light beam is an excimer laser beam having a wavelength of193 nm. The irradiated region is slit-like and covering part of apattern region of the reticle. The pattern corresponding to theslit-like portion is reduced in scale to be a quarter by a projectionoptical system 72 so as to be projected on a wafer 75 placed on a waferstage 73. The projection optical system 72 is arranged on a frame 76 ofthe exposure apparatus. By scanning the reticle and the wafer relativeto the projection optical system, the pattern region of the reticle istransferred on sensitive materials on the wafer. This scanning exposureis repeatedly performed on plural transfer regions (shots). Theprojection optical system 72 is required to have high resolution and thesupporting member for the lens thereof is demanded to have a structurewith high accuracies. Quartz and fluorite are used for the material ofthe lens. These lenses are supported as shown in FIG. 5, and in FIG. 5,when numeral 5 denotes a quartz lens, an alloy member 51 is an alloyincluding iron and nickel as principal ingredients such as invar; whenthe numeral 5 denotes a fluorite lens, it is preferable that an alloymember 51 be made of an alloy of copper and zinc as principalingredients such as brass. A material of the supporting member forsupporting the quartz lens may be preferably selected from a cordieritematerial including magnesium oxide and silicon oxide, a ceramic materialincluding alumina and silicon nitride, and a glass material having lowthermal expansion which is called Zerojule as the trade name.

A material of the member for supporting the fluorite lens may bepreferably selected from an alloy of iron-chromium-nickel such asso-called 18-8 stainless steel, an alloy of copper-tin-phosphorus, whichis called copper or phosphor bronze, an alloy ofnickel-iron-manganese-copper, which is called copper or white copper, analloy of nickel-chromium, and an alloy including aluminum as a principalingredient such as an aluminum die-casing alloy ofaluminum-silicon-copper.

As a material of the supporting member 53, a material having any thermalexpansion coefficient from iron down may be used. By the elastic member52, the unnecessary deformation of the lens due to the thermal expansioncoefficient difference between materials being different from each othercan be reduced. When the entire lens system is fixed to the frame 76 ofthe exposure apparatus body, the strain due to the fixing may beproduced in the lens supporting member 53; however, the elastic member52 has a function of reducing the strain from affecting the lens.Therefore, the lens supporting structure with high accuracies can beobtained, so that a lens system for obtaining resolution required formanufacturing semiconductors can be achieved.

In the above embodiment, the projection lens system of the semiconductorexposure apparatus has been described as an example; however, theinvention may be applied to a mirror other than a lens as an opticalelement. Also, it may be applied to an optical element in whichdeformation is a problem such as an optical element to which diffractionis applied.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

1. A supporting structure for supporting an optical element, saidsupporting structure comprising: a supported member including theoptical element; and a supporting member for supporting said supportedmember via a plurality of elastic members, each of which comprises aspring member, having elasticity in a radial direction of the opticalelement.
 2. A structure according to claim 1, wherein said spring membercomprises a plate-shaped spring member.
 3. A structure according toclaim 1, wherein each of said plurality of elastic members is contactedwith an outer surface of said supported member and an inner surface ofsaid supporting member.
 4. A structure according to claim 1, whereinsaid plurality of elastic members are disposed at intervals along aperiphery of said supported member.
 5. An exposure apparatus forexposing a wafer to light via a reticle, said apparatus comprising: anilluminating optical system for illuminating the reticle with light froma light source; and a projection optical system for projecting lightfrom the reticle onto the wafer, wherein at least one of saidilluminating optical system and said projection optical system comprisesa supporting structure, as defined in claim 1, for supporting an opticalelement.
 6. A method of manufacturing a semiconductor device, saidmethod comprising steps of: providing a reticle and a wafer into anexposure apparatus as defined in claim 5; and exposing the wafer tolight using the exposure apparatus.